Cronenberg's brainy approach makes this film fascinating but demanding as it traces the birth of psychoanalysis through the relationship and rivalry between Sigmund Freud and Carl Jung. The film radiates intelligence through clever direction and strong performances.

In 1904 Zurich, Jung (Fassbender) tests Freud's theoretical "talking cure" on manic patient Sabina (Knightley). And it works, revealing Sabina's own skills as a potential shrink. Two years later, Jung travels to Vienna to meet Freud (Mortensen), and they start a working friendship. But when Freud refers an outspoken patient (Cassel), Jung starts to question his morality. As a result, he starts an affair with Sabina, which is much hotter than his comfortable marriage to Emma (Gadon). But this causes him to question Freud's theories, leading to a clash of the titans.

The most enjoyable thing about this film is the way it encourages us to think for ourselves. Without taking sides or getting too academic about it, Hampton's script (his play The Talking Cure was based on John Kerr's book A Most Dangerous Method) provocatively explores psychoanalytical theory. Yes, there's rather a lot of talky dialog, both face-to-face discussions and detailed correspondence. And it often feels like a stage production. But it's also packed with bracing observations.

It also features terrific acting from Fassbender and Mortensen as men who are held together by their restrictive societies even as their beliefs transgress taboos. These are smart, tightly wound performances that reveal cracks in both men's personalities even as their theories are poised to forever change the way we look at the human mind. Knightley's performance is more difficult, as Sabina's wild insanity gives way to a fragile intelligence. Sometimes this feels like mad overacting compared to Jung's Protestant repression, but ultimately she's the only character who wears her emotions honestly.

As usual, Cronenberg designs the film to look almost mundane. The period design is unfussy, the lighting is a bit on the bright side and the costumes bind up the characters so they can barely move. But through the darkly layered performances and some clever directing and editing, it's fairly clear that Cronenberg is exploring his favourite place in the universe: the human brain. And we wouldn't want to go there with anyone else.